This invention relates to electrolytic bath vessel elements.
As an example and as is commonly known, the mercury process, the diaphragm process and the ion exchange membrane process are known for producing chlorine, hydrogen and sodium hydroxide by the electrolytic treatment of an aqueous solution of sodium chloride.
The mercury process is executed nowadays in an almost closed system. However, the problem of atmospheric pollution has not yet completely been solved and a considerable public fear in this respect still remains. Thus, those skilled in the art direct their most concern towards the diaphragm process as well as the ion exchange membrane process, using no mercury.
However, a grave quality problem exists in the sodium hydroxide products of the diaphragm process to such a point that the products contain a larger amount of common salt than that of the mercury process. In addition, there is a further problem that the electrolytic energy cost is considerably high.
In recent decades, ion exchange membranes characterized by superior selective permeability have been developed and the process using these membranes has been profoundly investigated and found that it can solve the public pollution problem which is inherent in the other two processes above mentioned. It is said that the products quality and the energy consumption rate are at least equal to or even higher than the other conventional processes.
As the anode used in this process, a dimensionally stabilized one is normally employed, and the membrane is highly thin. Therefore, the inter-electrode distance must be precisely kept and maintained in the electrolytic bath vessel.
Therefore, the bath vessel, especially its frame structure, and its composing frame elements must have a sufficient dimensional stability and a high degree of rigidity. It is further necessary to provide the bath vessel and its frame elements with a better fabricability and a better anticorrosion performance so as to assure favorable working ability in contact with the reaction mixture as well as the products during the course of the electrolysis. It is further necessary for the electrolytic bath vessel elements to have an efficient antipollution performance in such a sense that any detrimental and deteriorative substance to the ion exchange membrane can not practically be solved out from the elements under consideration.
As for the conventional bath frame material, polypropylene added with a proper amount of calcium silicate is broadly used as was disclosed in Japanese Open Patent Specification Sho-51-72973. However, it has been experienced with this kind of material that the mechanical strength is insufficient and the deterioration of the ion exchange membrane is appreciable.